The present invention relates to a system and method for controlling a limp-home function in an electronic throttle system, and more particularly, to a system and method for controlling the limp-home function adapted to prevent stalls by executing a proper limp-home control to cater to a running state of a vehicle when the electronic throttle system fails while the vehicle is in the running state.
In general, a throttle valve is linked to an acceleration pedal to adjust an output of an engine by controlling the amount of air to be drawn into a vehicle engine while the engine is running. When a driver manipulates an acceleration pedal, the open rate of the throttle valve correspondingly changes to control the quantity of air to be drawn into the engine.
Typically, the throttle valve is not connected to the acceleration pedal. Instead, based on signals generated by an Electronic Control Unit (ECU), the position of the throttle valve is determined through a throttle position sensor. The ECU calculates a target position of throttle valve to drive a driving motor and thus controls the throttle valve to obtain a target openness. The operational system thus described is called an electronic throttle system.
In general, a vehicle equipped with an electronic throttle system has a failure-safe function and a limp-home function. In the fail-safe function, the vehicle automatically performs safe running operations even if part of the system fails or malfunctions temporarily. In the limp-home function, a limp-home valve mounted on a throttle body is operated to take in a sufficient amount of air for temporary running of the engine so that the vehicle may run safely in spite of operational failure while the vehicle is running.
However, in conventional electronic throttle systems when there is a failure at the throttle valve position sensor. The output value of the sensor may be greatly changed, such that the electronic control system cannot perform a proper opening/closing of throttle valve, thereby leading to failure of engine.
The present invention provides a method for controlling the limp-home function in an electronic throttle system to prevent accidents that may occur due to unstable limp-home operation. Thus, a preferred method according to the present invention includes: detecting a malfunction of the throttle valve to determine whether the throttle valve has a problem of complete closure; determining whether a difference between a first output value set up as target by a throttle position sensor and a second output value measured by the throttle position sensor is greater than a first critical value and whether coolant temperature is larger than a reference value; determining whether an idle switch is turned on and whether engine revolution is less than a reference value; determining whether a reference period of time has lapsed and whether a third output value of the throttle position sensor has dropped below a second critical value and whether coolant temperature is higher than a reference value while the idle switch is turned on; and turning on a limp home valve if at least one of the conditions in the above steps is met.
Thus, according to a preferred embodiment of the present invention, if conditions provided at steps one through four are selectively determined and the limp-home valve is correspondingly controlled, it is possible for the limp-home valve to be properly controlled.
In a further preferred embodiment of the invention, a system is provided including an electronic control unit programmed to execute the above described steps.